Ultra low contact area end effector

ABSTRACT

The present invention comprises a vacuum end effector having workpiece supports that work in conjunction with distorted workpiece surfaces. In one embodiment, each workpiece support has the ability to gimbal and conform the workpiece surface in contact with an outer edge of the support. Each workpiece support preferably provides a knife-like contact edge to minimize the contact area between the support and the workpiece while still providing an effective vacuum area to hold the wafer securely on the support. In another embodiment, each workpiece support is replaceable without having to remove the end effector from the robot assembly

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. § 120 to U.S. patentapplication Ser. No. 11/404,536 entitled “Ultra Low Contact Area EndEffector”, filed with the U.S. Patent & Trademark Office on Apr. 14,2006, which claims priority to U.S. patent application Ser. No.10/888,819, entitled “Ultra Low Contact Area End Effector,” filed withthe U.S. Patent & Trademark Office on Jul. 10, 2004, which claimspriority to U.S. Provisional Patent Application Ser. No. 60/486,330,each of which is assigned to Applicants and incorporated herein byreference.

FIELD OF THE INVENTION

The present invention generally relates to an end effector for handlingsemiconductor workpieces. More particularly, the present inventionrelates to a vacuum gripping end effector that provides minimal contactbetween the workpiece supports and the backside of the workpiece.

BACKGROUND OF THE INVENTION

Conventional robotic vacuum chuck end effectors transfer significantparticulate contamination to the backside of the wafer at areas wherethe chuck contacts the backside of the wafer. Vacuum grips often causebackside contamination and/or damage to a wafer due to: (1) scratchingthe backside of the wafer—particularly from hard ceramic or anodizedaluminum contacts; (2) particles from the grip pad that are worn off andleft on bottom of wafer; and (3) particles that fall onto the grip padand are pressed onto bottom of wafer. Vacuum chuck end effectors alsohave difficulty achieving a low leak rate vacuum seal if the waferplaced on the end effector is warped or imperfectly aligned with the endeffector surfaces.

Edge support or edge grip end effectors minimize the amount ofparticulate contamination transferred to the backside of the wafer. Edgegrip end effectors, however, present difficulties in accurate wafer pickup and transfer and edge damage and/or contamination.

Gripping the perimeter edge of the wafer requires that structuralfeatures protrude from the upper surface of the end effector to asufficient height such that the protrusions extend above the top surfaceof the wafer being gripped. This method also requires features toactuate the protrusions, extending and contracting them as required,which increases complexity and failure modes. Further, either theprotrusion must be left as a remnant of a thicker piece of raw materialthan would otherwise be necessary, or the protrusions have to beattached to the end effector. The first method involves more rawmaterial and machining. Also, these protrusions are not replaceable. Thesecond method involves multiple parts and potentially complex permanentassembly methods, such as those discussed above. Edge grippingstructures, however, can be expected to be relatively thick, andtherefore difficult to maneuver through vertical stacking cassetteswhere the wafers are stored because the separation between wafers is onthe order of only about 5-10 mm.

There are increasing uses for ultra-thin wafers—low profile chipdesigns, direct mount on boards, etc. These wafers are often less than250 microns thick and are subjected to distortion and waviness. Thispresents challenges for handling thin substrates—which areconventionally not suitable for edge-grip technology end effectors.

One constraint with thin wafers includes ensuring that the vacuum sourcedoes not apply too much vacuum to the bottom surface of the wafer. Afull 10-15 psi vacuum source, for example, will likely cause the waferto warp. It is important, however, that the circular edge conform to thebottom surface of the wafer.

Accordingly, there is a need for a low profile vacuum end effector thatincludes workpiece supports that work in conjunction with distortedwafer surfaces. It is also desirable for the end effector to accommodatea wide variety of support materials and reliably retain the pads inplace, while permitting damaged or worn supports to be readily replaced.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide an end effector thateliminates or greatly minimizes particulate transfer to the backside ofthe wafer. In one embodiment, the workpiece chucks or supports include acircular knife-like edge that provides the only contact between thewafer support and the wafer.

Another aspect of the present invention is to provide an end effectorthat includes self-aligning vacuum chucks or supports. The workpiecesupports accommodate any lack of wafer planarity and work in conjunctionwith distorted wafer surfaces. The supports provide an effective vacuumseal under the conditions of lack of planarity between the backside ofthe wafer and the vacuum supports.

Still another aspect of the present invention is to provide an endeffector that includes replaceable workpiece supports. In oneembodiment, each workpiece support may be readily exchanged withouthaving to remove the end effector from the robot assembly. The workpiecesupports may comprise, by way of example only, a ceramic, a plastic, ora metal. The workpiece support preferably comprises a material suitedfor the type of workpiece that end effector will be handling.

Another aspect of the present invention is to provide an end effectorthat minimizes or eliminates the amount of deformation and/or stressinduced into the workpiece transferred by the end effector, withparticular respect to fragile workpieces (e.g., thin wafers, SOI wafers,etc.). Even though the contact area between the workpiece support andthe wafer is very small, the workpiece support provides a sufficientlylarge effective vacuum surface to hold the workpiece on the endeffector.

Still another aspect of the present invention is to provide an endeffector that provides a choice of manufacturing approaches for theworkpiece supports. The workpiece supports, by way of example only, maybe manufactured through a machining, injection molding, plating, orchemical milling process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the present invention;

FIGS. 2A-2B are side sectional views of an embodiment of the presentinvention, illustrating one embodiment of a workpiece support;

FIG. 3 is a detailed perspective view of the workpiece support shown inFIGS. 2A-2B;

FIGS. 4A-4B are representative drawings, illustrating the contact areabetween a wafer and a workpiece support for an end effector according tothe prior art and an end effector, utilizing the workpiece supportaccording to the present invention;

FIG. 5 is a top view of an embodiment of the present invention;

FIG. 6 is a side view of an embodiment of the present invention,illustrating the knife-like contact between a workpiece support and awafer;

FIG. 7 is a side cut-away view, illustrating another embodiment of aworkpiece support, according to the present invention;

FIG. 8 is a partial side view of the workpiece support shown in FIG. 7;

FIG. 9 illustrates another embodiment of a workpiece support, accordingto the present invention;

FIG. 10 is a side cut-away view of another embodiment of the presentinvention, illustrating a wafer support retained by a foam ring; and

FIG. 11 is a side cut-away view of another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The bottom surface of end effector, in many embodiments, comprises amembrane. The membrane seals the bottom surface of the end effector andforms a vacuum cavity under the wafer support.

The present invention will now be described with reference to FIGS.1-11. In general, the present invention comprises an end effector 100having a combination of workpiece or wafer supports that contact thewafer in zones where particulate contamination is less critical, suchas, for example, the outer edge of the wafer. In another embodiment, oneor more wafer supports are used with accommodation for lack ofco-planarity achieved by allowing the support(s) to tilt as required.FIG. 1 illustrates that the end effector 100 includes two wafer supports114 and 116 in front of the center of gravity of the wafer 108. It iswithin the spirit and scope of the invention to have more than or fewerthan two supports on the end effector.

A very low contact area circumferential sealing feature is utilized. Thewafer supports 114 and 116 provide a knife-edged or small radius contactgeometry, thus reducing the contact area between the wafer support chuck114 and 116 and the wafer's backside 130 (and the potential forparticulate transfer).

The end effector 100, in a first embodiment, includes a first end 104adapted to secure to a wafer handling robot and a second end or platen106 for supporting the wafer 108. The platen 106 includes a first finger110 and a second finger 112. The first and second fingers 110, 112 arepreferably spaced apart so that the first wafer support 114 and thesecond wafer support 116 contact different areas of the backside of thewafer 108. For ease of describing the embodiments of the invention,wafer support or chuck 114 will often be referenced throughout. Anyattributes of wafer support or chuck 114 of course apply to wafersupport 116. In this embodiment, the wafer 108 is also supported byfirst and second edge supports 118, 120. The platen 106 may include anynumber of fingers.

FIGS. 2A-2B illustrates that the first and second edge supports 118, 120preferably only contact the wafer 108 along its edge or periphery. Eachedge support includes a wafer support surface 122 and a backstop 124.The wafer support surface 122 is stationary and preferably comprises alow friction non-particulate generating material.

The end effector 100 includes a support retention area 126 forsupporting each wafer support 114 and 116. The support retention area126 is a partial bore or recessed pocket. The support 114 and 116 isused to support the wafer 108 and keep the wafer 108 from contacting thesurface 128 of the end effector 100. By preventing the wafer 108 fromcontacting the top surface 128 of the end effector 100, the wafer 108 isprotected from contamination by the end effector 100 during handling.

The pivoting ball and socket joint 146 eliminates or greatly minimizesthe lateral scrubbing of the wafer support chuck contact area 136 due tothe tilting action.

FIGS. 2A-2B illustrates a first embodiment of a wafer support 114. Inthis embodiment, the wafer support 114 has a circular raised edge 132that contacts the wafer's backside 130. The central region 134 of thewafer support chuck 114 is recessed below the contact portion 136 of theraised edge 132 so that only the contact portion 136 contacts thewafer's backside 130. The center region 134 includes a bore 138 thatextends completely through the wafer support 114. The bore 138 extendsfrom the bottom surface 142 of the wafer support 114 toward the centralregion 134. When the bore 138 approaches the central region 134, thebore 140 begins to taper outward such that the diameter of the bore 138at the central region 134 is larger than the diameter of the bore 138 atthe bottom surface 142.

The wafer support 114 and 116, therefore, are only in contact with thewafer by a distance d1 (see FIG. 4B). The raised edge 132, by forming aseal with the wafer's backside 130, forms a vacuum seal with the wafer'sbackside 130 across an effective diameter d (see FIG. 2A). A vacuumpassage 144 (see FIG. 5) travels through each finger 110, 112, andterminates substantially beneath the wafer support 114 and 116. FIG. 2Billustrates that a passageway from a vacuum source is provided by thevacuum passage 144 and the bore 138. In a preferred embodiment, thewafer support 114 and 116 forms a substantially air-tight seal with thewafer's backside 130 and the pivot socket 146 when the vacuum and sourceis activated or turned on.

The circular edge 132 must have a diameter large enough so that thevacuum provides a force large enough to hold the wafer 108 on the wafersupport 114 and 116. A smaller diameter support, however, betteraccommodates any localized non-flatness of the wafer. If, for example,the wafer support 114 and 116 includes a circular edge 132 four inchesin diameter, the wafer support 114 and 116 may still leak even with thegimbaling features. By achieving a good seal with a small diametercircular edge, the wafer support imparts maximum efficiency of theavailable vacuum force.

The wafer supports 114 and 116 and the edge supports 118 are locatedsuch that the wafer's center-of-gravity falls within the supports. Thisconfiguration ensures a stable condition for the wafer 108 prior toactivating the vacuum source. The wafer supports 114 and 116 preferablycomprise a low friction material so that the weight of the wafer 108 issufficient to gimbal the wafer support chuck 114 and 116 to an optimumconformance to the wafer's bottom surface.

The wafer support 114 and 116 also prevents any lateral motion by thewafer 108 or the chuck 114 itself when the vacuum is applied. The lackof motion is particularly important when high accuracytransfers/hand-offs are required, such as between a wafer prealigner anda metrology or process station. In the semiconductor industry, transferaccuracy requirements are currently less than 25 microns and will likelycontinue to decrease.

The wafer supports 114 may comprise different material (e.g., ceramicfor high temperature applications) and are easily replaceable. Anoperator may change out a wafer support 114 without affecting thestructure of the end effector 100.

The actuation of vacuum simultaneously pulls the wafer's backside 130against the sealing surface 136 of the support 114 and brings thesupport 114 into contact with the pivot socket 146. The pivot socket146, by way of example only, primarily serves four functions. (1)enables tilting motion of the wafer support chuck 114 for optimumsealing between the wafer support chuck 114 and the backside of thewafer; (2) provides vertical support for the wafer support chuck 114 anda wafer 108 seated on the chuck 114; (3) provides self-actuated vacuumsealing of the pivot socket 146 due to force exerted by projected areawhen vacuum is applied; and (4) provides accurate and unambiguouslocation of a wafer 108 seated on the wafer support chuck 114 due to thechuck's self-centering design.

The geometry of the wafer support 114 provides a center of rotation thatis coincident with the wafer support plane. This feature is defined aszero scrub radius. The wafer support 114 and the pivot socket 146comprise a gimbal joint. A gimbal joint represents a composite jointwith three rotational degrees-of-freedom.

If the wafer support 114 is gimbaling or pivoting, the instantaneouscenter of gimbaling is where the centerline is drawn (centerline ofspherical surface). If the center of rotation of the wafer support 114is positioned correctly, the center of rotation of the wafer support 114is coincident with wafer support plane. Small angles of deflectioncreate substantially no lateral sliding of the wafer support 114 againstthe wafer 108, even if there is angular misalignment between the wafersupport 114 and the wafer 108. The center of rotation of the wafersupport 114 may be higher/lower than that shown in FIG. 2B, however, thewafer support 114 will likely generate more particulates.

The wafer support 114 is seated in the pivot socket 146. Once a vacuumsource is activated, the projected area of the wafer support 114 incontact with the pivot socket 146 sucks the wafer support 114 againstthe pivot socket 146. An o-ring, having a diameter slightly smaller thanthe diameter of the wafer support 114, ensures that the wafer support114 remains in the pivot socket 146. The retaining feature may alsocomprise a coil or leaf spring.

Each wafer support 114 may wiggle because there is a clearance betweenthe o-ring/clip and the edge of the support. The wafer support 114conforms to the bottom surface of a wafer seated on the end effector.The wafer support 114, once the vacuum source is activated remainssubstantially in the same position until the vacuum source is turnedoff. If a wafer 108 settles down on the wafer support 114 at an angle,for example, the wafer support 114 will comply with the backside of thewafer (e.g., the wafer remains at the angle relative to the endeffector).

When the vacuum source is turned on, for example, the circular edge 132of the wafer support 114 forms a seal with the bottom surface of thewafer. For example, if the end effector 100 raises up to the backside130 of the wafer 108, the wafer support 114 gimbals until the circularedge 132 makes 360° contact with wafer backside 130. The entire circularedge 132 preferably forms a seal with wafer backside 130. As previouslydiscussed, the contact surface between the circular edge 132 and thewafer 108 should be knife-like (e.g., contact distance of less than 0.05mm). Basically, the contact area between the circular edge 132 and thewafer 108 is preferably very small.

FIGS. 4A-4B illustrate the contact area between a wafer support 114 andthe backside of the wafer. A conventional wafer support, as shown inFIG. 4A, includes a circular edge 36, having a width d3. Thus, a largecontact area is formed between the wafer support and the wafer 8. FIG.4B illustrates the knife-like contact edge 136 of a wafer support 114according to one embodiment of the present invention. The contact edge136 only contacts the backside 130 of the wafer 108 by a distance d1. Incomparison with the conventional wafer support, the distance d1 is muchsmaller than the distance d3—achieving a minimal contact area betweenthe wafer support 114 and the wafer 108.

FIG. 5 illustrates one embodiment of a vacuum path 144 that provides apassageway between a vacuum source and the cavity located beneath eachwafer support 114. The end effector 100 illustrated in FIG. 5 includestwo wafer supports 114. It is within the scope and spirit of theinvention for the end effector to include more or less than the twowafer supports 114.

FIG. 7 illustrates another embodiment of a wafer support. The wafersupport includes a raised central peak 236, a clearance area 240surrounding the raised central peak 236, and a raised edge 238. Vacuumis fed through the vertical holes in wafer support. The cross sectionalarea of the vertical holes is preferably greater than area between theraised edge 238 and the bottom surface of the wafer 130 (defined as a“leakage zone”). The central peak 236 is preferably the only area ofcontact between the wafer support and the wafer 108. The central peak238 therefore provides a minimal contact area to support the wafer. Theleakage zone creates a pressure drop across the raised edge 238providing reduced pressure in the clearance area that holds the waferdown. The leakage zone may also create a Bernoulli effect—creatingnegative lift to hold the wafer down.

A second embodiment of a wafer support chuck is illustrated in FIG. 7.Instead of edge supports, the wafer support chuck 214 includes a centercontact surface or ridge 232, or other support element geometries, tosupport the backside of the wafer. The center contact ridge 232 is theapex of the central region 234 of the wafer support chuck 214. Oneembodiment of the central region 234 comprises a conical section, asshown in FIG. 8, yet may comprise other geometries, The chuck conceptcould also be used in non-robotic applications, for example, on processor metrology wafer holding stations. The chucks could be arranged in anon-planar manner to produce a curved or cylindrical wafer surface.

FIG. 8 illustrates that the contact ridge 232 is preferably a roundedsurface, having a radii R. Accordingly, the contact ridge 232 and thewafer's backside 130 form a contact area d. The wafer support chuck 232also includes an outer contact area or ridge 236. The outer contactridge 238 preferably does not contact the wafer's backside 130 when awafer 108 is seated on the chuck 114 to minimize the contact areabetween the chuck 114 and the wafer 108. The outer ridge 236 may,however, contact the backside 130 if the wafer 108 or the chuck 114tilts.

Each wafer support chuck 114 may comprise a wear resistant polymer suchas, but not limited to, Teflon or PEEK. The difficulty of using suchplastics is that the plastics are soft and easily damaged so that a sealbetween the contact area suction cups and the backside of the wafer ishard to achieve. This difficulty is generally compensated for by using alarge contact surface area. But a large contact surface area is morelikely to collect particles and pass them onto the wafer backside 130.In one embodiment, each chuck 114 includes a thin, knife-edge contactthat is extremely flat at the contact point and is damage resistant. Byusing removable ridged rings or chucks as contact pads, a durable yetnon-abrasive knife-edge thin contact seal can be achieved practicallyand cost effectively.

The wafer support chuck 114 may be made from a variety of materials.Desirable characteristics include low vapor pressure at temperature,high hardness, and inertness. Typical materials include metals such asstainless steel, crystals such as quartz, ruby, and sapphire, andceramics such as silicon carbide, silicon nitride, and tungsten carbide.Because some of these materials are rather brittle and difficult tomachine, cylindrically shaped pins of the correct axial length can beadvantageously used in accordance with the invention. These materialsexhibit a relatively high coefficient of friction and better “grip” thewafer during acceleration and deceleration of the end effector by therobot, protecting against slippage.

In an alternative embodiment, the end effector support plate 106 ismilled or ground with three round areas 126 that are recessed. A vacuumis routed through the end effector 100 and terminates at the centerregion of the round pockets 126. Replaceable wafer supports are placedin the pockets and held with a thin adhesive. Alternatively, vacuum maybe routed to each cup 126 independently so that a leak in one does notreduce the vacuum grip of the others.

The end effector 100 may be made of any suitable material. Desirablecharacteristics include low weight and structural stability at hightemperature. Typical materials include metals, such as stainless steel,aluminum, titanium, molybdenum, ceramics, composites and combinationsthereof The end effector 100 can be manufactured from machined platestock or can be pressed powder materials. Because the invention does notrequire bonding or otherwise attaching the wafer support chuck 114 tothe end effector 100, any combination of pad material and end effectormaterial can be used. Also, because the chucks 114 can be readilyremoved and replaced, worn or damaged, chucks 114 can be changedquickly, without rework of or damage to the end effector 2.

Several designs for the rings and chucks 114 and 116 are possible andcould be selected depending on the demands of the application. Anexample of ring and chuck designs are:

Design #1: PEEK or another stable, strong, clean polymer is turned on alathe into a number of shapes (see FIG. 10B). The thin contact edge maybe flat and parallel with the bottom surface of the wafer.

Design #2: The same chuck may also be made out of metal, either on alathe or with a forming process such as sintered powder forming. Thismetal base is then coated with a thin (e.g., less than 0.001″) Tefloncoating. The edge contact is far more durable and precisely flat than ifthe part were Teflon alone. A good seal can therefore be maintained withthe backside of the wafer with a minimal contact area. In a preferredembodiment, only the non-abrasive chemically inert pure Teflon comes incontact with the wafer.

Design #3: A hard elastomer like 100 durometer Viton® is molded in anyshape, or with a flat top. This is appropriate for applicationsrequiring high grip strength where cleanliness is not as critical.

Because of the low contact area, the rings are more likely to wear outor become damaged than normal vacuum pads. This is mitigated by the factthat the rings are easily installed and removed and can be replacedduring scheduled maintenance. To make removal of the rings easy, a holeis provided on the back side of the end effector for each ring so thateach ring can be pushed out with a piece of wire (e.g., a paper clip).

The surface can then be cleaned and another ring installed. A thindouble sided adhesive tape is attached to the bottom surface of thering. The rings are provided on a backing sheet from which they can beeasily removed without wrinkling the adhesive. They are then placed intothe pocket that locates them centered over the vacuum hole.

FIG. 10 illustrates that the rings may be attached via a foam orotherwise compliant layer to allow the rings to tilt slightly tocompensate for un-flat wafers or end effector paddles. The contactdiameter of each ring is preferably large enough to hold a wafersecurely on the end effector while the wafer is in transport. An endeffector that includes two wafer supports, for example, requires thatthe contact diameter of each chuck be approximately 0.50″ in order toprevent the wafer seated on the end effector from sliding off the endeffector during transport.

Vacuum may be routed to each chuck independently so that a leak in onedoes not reduce the vacuum grip of the others.

For 200 mm cassettes and 300 mm FOSB, the end effector vertical profileis preferably less than 3-3.5 mm to be able to enter between wafers thatare stacked in a cassette at ¼″ or 6 mm pitch with acceptableclearances. It is very difficult to manufacture a ball and socket designusing a separate socket bushing part and using an external retainer partthat would fit in this profile.

The contact chuck is still made from relatively rigid plastic such asPEEK, PET, Ultem, Vespel, or Torlon (could also be metal or ceramic withappropriate surface treatment). It is supported via a compliantelastomer ring. The elastomer allows a small amount of angular tilt ofthe rigid chuck.

FIGS. 10-11 illustrate additional ways for a chuck to pivot as analternative to the gimbaling ball and socket shown in the preferredembodiments. FIGS. 10-11 illustrate alternative lower profile and/orchucks that are cheaper to manufacture. These chucks comprise ofdeformable, yet still hard, material. These chucks, however, do notprovide a full gimbaling range of motion (e.g., three degrees of freedom)—the chucks primarily tilt one way or another. FIG. 10 illustrates afoam ring that retains the wafer support. FIG. 11 illustrates an o-ringthat retains the wafer support. The o-ring may snap into a groove or besecured to the end effector by a retaining ring or device. The foam ringand the o-ring allow the wafer support or chuck to flex or tilt. FIG. 9provides a perspective view of the chucks shown in FIGS. 10-11 placed inan end effector.

In one embodiment, the elastomer is a foam ring with adhesive on bothsides, such as 3M's VHB polyurethane foam tape with acrylic adhesive.The foam ring provides a seal and attaches the chuck to the supportplate. The chuck is constrained in X, Y and Z directions by a ball incone or ball in socket feature. As illustrated, the chuck has a smallspherical protrusion which engages a conical surface in the supportplate. In another embodiment, the elastomer is an o-ring. The chuck isretained by a standard retaining ring.

According to the invention, the end effectors can be made relativelythin, on the order of about 0.1 inches in thickness to accommodate highdensity semiconductor wafer storage cassettes. The end effectors can besized to support and transport any size wafer, such as conventional 300mm, 600 mm, and 900 mm diameter wafers. Also, the end effectorsaccording to the invention are relatively light, minimizing thecantilever loading and resultant sagging or deflection of the roboticarm when fully extended to retrieve or replace a wafer in a storagecassette or carousel. Accordingly, the end effector can be accuratelypositioned and mishandling of wafers is minimized.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to precise forms disclosed. Obviously, many modifications andvariations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiment and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

1. An end effector for transporting a semiconductor workpiece,comprising: a low-profile body having a proximal end and a distal end,said low-profile body including a recessed pocket in fluid communicationwith a vacuum channel passing through a portion of said low-profilebody; a support pad partially seated within said recessed pocket, saidsupport pad having a body with a central workpiece contact surface, araised edge and at least one vacuum aperture passing through said body,wherein when a workpiece is seated on the end effector, a bottom surfaceof the workpiece contacts said central workpiece contact surface of saidsupport pad and a gap exists between said raised edge of said supportpad and the bottom surface of the workpiece.
 2. The end effector asrecited in claim 1, wherein a diameter of said at least one vacuumaperture is greater than a height of the gap between said raised edgeand a bottom surface of the workpiece.
 3. The end effector as recited inclaim 1, wherein said at least one vacuum aperture comprises a firstvacuum aperture and a second vacuum aperture.
 4. The end effector asrecited in claim 3, wherein a height of the gap between said raised edgeand a bottom surface of the workpiece is less than the diameter ofeither said first or said second vacuum apertures.
 5. The end effectoras recited in claim 1, wherein said support pad comprises a polymer. 6.The end effector as recited in claim 1, wherein said support padcomprises a circular geometry.
 7. The end effector as recited in claim1, wherein said central workpiece contact surface comprises a roundedsurface.
 8. The end effector as recited in claim 1, wherein saidrecessed pocket is located in said distal end of said low-profile body.9. The end effector as recited in claim 1, wherein said recessed pocketis located in said proximal end of said low-profile body.
 10. The endeffector as recited in claim 8, further including a second recessedpocket located in said proximal end of said low-profile end effector.11. The end effector as recited in claim 10, further including a secondsupport pad partially seated within said second recessed pocket.
 12. Theend effector as recited in claim 9, further including a second recessedpocket located in said distal end of said low-profile end effector. 13.The end effector as recited in claim 12, further including a secondsupport pad partially seated within said second recessed pocket.
 14. Anend effector for transporting a semiconductor workpiece, comprising: alow-profile body having a proximal end and a distal end, the low profilebody including a recessed pocket having an opening in a bottom surfaceconnecting said recessed pocket with a vacuum channel passing through aportion of said low-profile body; a support pad partially seated withinsaid recessed pocket, including: a central portion having a first end, asecond end and a vacuum channel extending between said first and secondends, said central portion extending through said opening in saidrecessed pocket such that said first end of said central portion islocated within said vacuum channel; and a body extending outward fromsaid second end of said central portion, said body transitioning into anelevated edge contact surface; and a retaining device, affixed to saidfirst end of said central portion, for retaining said support pad withinsaid recessed pocket.
 15. The end effector as recited in claim 14,wherein said elevated edge contact surface comprises a circulargeometry.
 16. The end effector as recited in claim 14, wherein saidsupport pad comprises a polymer.
 17. The end effector as recited inclaim 14, further comprising: a deformable support for separating saidbody from a bottom surface of said recessed pocket.
 18. The end effectoras recited in claim 14, wherein the recessed pocket is located at thedistal end.